There are several ways to insert functions. Before anything, you need to make sure your cursor is in the cell in which you want the result. Once there, choose one of the methods below to insert your function:
The Insert Function dialog box that appears gives you a list of operations that Excel can perform.
Choose a category from the Select a category: pulldown (which includes an option to show all), and then a particular function from the Select a function: pulldown.
Another dialog box opens which asks you to select the cells you would like to involve in the formula. To select, use the mouse to click on the first cell and drag through the cells you would like to add. Note that for each function, this second window will look different.
If you’re not sure how to use a particular function, you can click the "Help on this function" link on the bottom of the Insert Function dialog box, and that will bring up Excel’s Help.
Once the function is in the cell, you can copy and then paste it into another cell to do the same function for that different range of cells. You can also use the AutoFill command (click cell with the function, then drag to the right or down). The formula adjusts automatically for the new values.
As mentioned before, if you want a constant reference (for example, each column should be divided by a certain cell’s data), add a dollar sign ($) in front that cell’s reference in the Formula bar. For example, if =D8*$P$8 is in the Formula bar and you AutoFill from this cell, the next cell would read =D9*$P$8, changing the first cell, but keeping the second cell reference constant – otherwise, it would read =D9*P9.